Preparation of photographic developers



Patented Mar. 27, 1928. I

PATENT OF F ICE."

PIERRE SCHESTAKOFF, OF PARIS, FRANCE.

PREPARATION F PHOTOGRAPHIC DEVELOPERS.

No Drawing. Application filed April-29, 1925, Serial No. 26,804, and in Germany May 12, 1 924.

In the present state of the art there is no method known in photography for obtaining automatic rectification of errors 1n exposure.

The processes utilized up,v to the present for efiecting such rectifications consist simply in modifications in the composition or concentration of the developers being used, during development, the result being that these rectifications depend merely upon the experience and skill of the operator. In

many cases, as for instance during the development of a film in which normally exposed, over exposed and under exposed portions are all present without it being known in which portions of the filmthe defective sections are to be found, rectifications are impossible. 0'

When using ordinary plates in the case of which there are greatly over exposed or under exposed portions or which have been exposed to a bright facing light, there is no process which enables a good negative to be obtained, that is to say a negative which is not clouded, fogged by the sun or showing cals as for instance H Hydroxylamine sulphonic acid N OH SOaH.

Hydroxylamine disulphonic acid N-SO3H SOzH.

. I v Hydroxylamine isodisulphonic acid N-OSOaH SOaH.

SOaH Hydroxylamine trisulphonic acid N-OSOzH SOaH.

Nitrilosulphonic acid N (SO3H) Derivatives of hydroxylamine can also be used in which one atom of hydrogen is re- .placed by an organic-radical of thetype C.H -C H etc., such as H 1) RN/ on. v 1

, our

osom.

. so 11 4 R=I-{ a I so|n. Finally derivatives of hydroxylamine may 'be employed in which the hydrogen, atom is replaced by an organic radical of the type C H CO, such as hydroxamic acid for instance v v Each of these substances or their salts when introduced into the composition of the developer gives it new properties by means of which, during development, without modifying the composition or concentration, defects of exposure may be suppressed as also the phenomena of fogging and halo when exposures are taken facing a bright light. In general the violent contrasts between light and shade are equalized. At the same time the said substances reduce to so great an extent the sensitivity of the silver haloids that it is possible to develop in a bright red light or even in a yellow light.

By way of example, the following composition of a developer made according to the invention is now given.

Grammes. Water 1,000 Hydroquinone- 5 Sodium sulfite 20 Sodium hydroxylamine isodisulphonate 5 40 Sodium carbonate Potassium bromid 1 What I claim and desire to secure by Letters Patent of the Un ted States of America 1. A photographic developer formed by mixing with substances constituting an ord1- nary developer, nitrous acid salts and sulphurous acid salts, substantlally as described.

2. A photographic developer formed by ine by sulphonicradicals, substantially as mixing with substances constltuting an ordidescribed. nary developer, the reaction products of 4. A developer for photographic purposes, nitrous acid salts with sulphurous acid salts formed by mixing with substances-'constiimt- 15 substantially as and for the purposes deing-Ian ordinary developer,hydroxylamine scribed. derivatives in which one atom of hydrogen 3. A developer for photographic pur; is replaced by an organic radical of the type poses, formed by mixing with substances CH -C H constituting an ordinary developer, hy- In witness whereof I aflix my signature. droxylamine derivatives obtained by replacing the hydrogen atoms of hydroxylam- PIERRE SOHESTAKOFF. 

